1. Field of the Invention
The invention relates to a process for the production of 6-hydroxynicotinic acid by enzymatic hydroxylation of nicotinic acid.
2. Prior Art
Processes are known which make possible the production of 6-hydroxynicotinic acid by means of live microorganisms of the genera Pseudomonas, Bacillus or Achromobacter (see Swiss Patent Nos. 658,866 and 658,867). Such processes use a biomass suspension of the corresponding microorganisms, which are obtained in a separate process step by multiplication of a starter culture. The actual hydroxylation takes place either in a batch process with single addition of nicotinic acid as the sodium salt (batch process, see Swiss Patent No. 658,866), or in a continuous process in which the nicotinic acid is added as the (easily soluble) magnesium or barium salt and the 6-hydroxynicotinic acid is isolated as slightly soluble magnesium or barium salt (see Swiss Patent No. 658,867). Since the multiplication of the microorganisms is inhibited by the nicotinic acid concentrations used in such processes, it is necessary in both processes to obtain the total amount of the effective biomass in an upstream process step. Moreover, the known processes for the enzymatic production of 6-hydroxynicotinic acid have still other drawbacks. The continuous process according to Swiss Patent No. 658,867 yields magnesium or barium salts from which the 6-hydroxynicotinic acid is released by acid addition. In this case, the magnesium or barium salt of the added acid results, which has to be disposed of as waste. But especially soluble barium salts are highly toxic for higher organisms. With prolonged continuous operation, moreover incrustations by the crystallized salts or foreign infections easily occur.